1. Field of the Invention
The present invention is relates to an apparatus for producing polycrystalline silicon producing rods of polycrystalline silicon by depositing polycrystalline silicon on a surface of heated silicon rod in a reactor.
Priority is claimed on Japanese Patent Application No. 2010-108472, filed on May 10, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
A producing apparatus by the Siemens process is known as a producing apparatus of polycrystalline silicon. In the producing apparatus of polycrystalline silicon, a plurality of silicon seed rods are vertically set in a reactor and electric current is supplied to heat these rods. Raw gas including silicon compounds, such as chlorosilanes, and hydrogen is supplied into the reactor so as to bring the raw gas into contact with the heated silicon seed rods. As a result, polycrystalline silicon is deposited on the silicon seed rods by thermal decomposition reaction and the hydrogen reduction of the raw gas, so that the silicon seed rod grows into a rod-shape.
Conventionally, in the above-mentioned producing apparatus of polycrystalline silicon, a wall of the reactor used to be formed from quartz. However, as described in U.S. Pat. No. 4,311,545 and Japanese Unexamined Patent Application, First Publication No. 2009-173492, as the size of the apparatus is increased, the wall of the reactor is made from metallic materials such as stainless steel, nickel-base alloy or the like. Since the inner of the reactor is heated up to high temperature of around 1000° C. while producing polycrystalline silicon, in order to prevent contamination by impurity to polycrystalline silicon from the metallic materials, the temperature of the wall which is in contact with the atmosphere in the reactor should be kept lower than a certain restrictive temperature, for example, 300° C.